1. Technical Field
The present invention relates generally to a semiconductor device and a method for fabricating the same, and more particularly to a semiconductor device that comprises a vertical channel transistor and a method for fabricating the same.
2. Related Art
In general, a semiconductor, as a material which belongs in an intermediate range between a conductor and a nonconductor by material classification depending on electric conductivity, has similar properties as a nonconductor at a pure status. However, the electric conductivity of a semiconductor material may be increased by the addition of impurities or by other manipulations. Such semiconductor material is used for a semiconductor device such as a transistor by adding impurities and connecting the conductor. A semiconductor apparatus refers to an apparatus manufactured using such a semiconductor device to have various functions. A representative example of a semiconductor apparatus is a semiconductor memory apparatus.
A semiconductor memory apparatus comprises a plurality of unit cells including a capacitor and a transistor. The capacitor is used to store data and the transistor is used to transfer data between the capacitor and a bit line in response to a control signal (a word line) using a semiconductor property in which electric conductivity changes according to conditions. The transistor has three parts including a gate, a source, and a drain. Electric charges move between the source and drain according to the control signal input to the gate. The electric charges move between the source and drain through a channel region using semiconductor properties.
When a conventional transistor is fabricated on a semiconductor substrate, the gate is formed over the semiconductor substrate and then the source and drain are formed by implanting impurities into the semiconductor substrate. In this case, a space between the source and the drain below the gate is a channel region of the transistor. Such transistor having the vertical channel region occupies a given area of the is semiconductor substrate. In complicated semiconductor memory apparatuses, it is difficult to reduce a unit size of a transistor in the semiconductor memory apparatus.
If the unit size of a semiconductor memory apparatus is reduced, the number of semiconductor memory apparatuses that can be produced per wafer may be increased to improve productivity. In order to reduce the unit size of the semiconductor memory apparatus, various methods have been suggested. One of these methods uses a vertical transistor having a vertical channel region instead of a conventional horizontal transistor having a horizontal channel region.
In the vertical transistor, a source and a drain are formed in the upper and the lower of pillars extended vertically, and a channel is formed between the source and the drain in up-and-down directions (vertically) along the pillars. The advantage of the vertical transistor is that a semiconductor cell may be manufactured in a narrower area than the horizontal transistor.